Strapping machines apply a steel or polymeric strap in a sealed tensioned loop about a package to securely bind the package for shipping, storage and merchandising. Automatic strapping machines generally comprise an automatic strap feeding mechanism that initially feeds a strap to a strap application assembly comprising an annular channel where the strap is formed in a loop which surrounds a package to be bound. An automatic strap tensioning mechanism then applies a tension to the strap so that the strap application assembly may form a strap seal to securely bind the package. Steel straps are typically sealed with a metal clip and polymeric straps are typically sealed by a weld formed with a healed blade or by friction. It has been suggested to feed a strap to a strap application assembly by frictionally engaging the strap between a pair of counter-rotating rollers rotated by a motor driven shaftjournaled to a frame. Likewise, it has also been suggested to apply a tension to a strap by frictionally engaging the strap between a pair of counter-rotating rollers that draw the strap in a light loop about the package. For example, U.S. Pat. No. 3,232,217 to Itarmon el al. discloses a strap feeding and tensioning mechanism comprising two pair of counter-rotating rollers mounted on a bracket that may be positioned to frictionally engage a strap for feeding or tensioning the strap in a strap application assembly. Automatic strapping machines frequently encounter problems feeding the strap to the strap application assembly. For instance, the strap may not properly feed along the annular channel or the strap may not be securely retained by the strap application assembly during tensioning of the strap. A strap not properly fed to the strap application assembly or a strap not securely retained by the strap application assembly during tensioning of the strap must be retracted from the strap application assembly and then re-fed by the strap feeding mechanism. Known strap feeding and tensioning mechanisms also have the disadvantage that they subject the strap to considerable mechanical stress that may result in breakage of the strap during application of the strap or during handling of the bound package. Mechanical stress is not limited to the strap but also to the strap feeding and particularly the strap tensioning mechanism which may be subject to considerable frictional forces during feeding and tensioning of the strap. There exists therefore a demonstrated need for an advancement in the art of feeding and tensioning a strap in a strapping machine.
It is an object of the present invention to provide a novel strap feeding and tensioning apparatus.
it is also an object of the present invention to provide a novel strap feeding and tensioning apparatus the automatically re-feeds a strap not properly fed to a strap application assembly in the first instance.
It is also an object of the invention to provide a novel strap feeding and tensioning apparatus that is economical to manufacture and operate.
It is another object of the invention to provide a novel strap feeding and tensioning apparatus that minimizes damage to a strap during feeding and tensioning of the strap.
It is a further object of the invention to provide a novel strap feeding and tensioning apparatus having a cam actuated feed roller that feeds the strap to a strap application assembly.
It is a farther object of the invention to provide a novel strap feeding and tensioning apparatus having a cant actuated tensioning roller that applies a fixed or variable tension on the strap after the strap is formed in a loop in a strap application assembly.
It is a further object of the present invention to provide a novel strap feeding and tensioning apparatus that reduces an amount of energy required to feed and apply tension to the strap.
It is yet a further object off the invention to provide a novel strap feeding and tensioning apparatus that reduces stress on the feeding and tensioning apparatus and thereby increases the reliability and lifetime of the strap feeding and tensioning apparatus.
Accordingly, the present invention is directed toward a novel method and apparatus for feeding and tensioning a strap in a power strapping machine. The apparatus includes a strap feeding mechanism, a strap tensioning mechanism, and a pivoting roller carriage having a cam follower. The strap feeding mechanism is comprised of a fixed feed drive roller and a feed follow roller disposed on the pivoting roller carriage. The strap tensioning roller is comprised of a fixed tension drive roller and a tension follow roller also disposed on the pivoting roller carriage. The pivoting roller carriage is pivoted by a feeding and tensioning cant having a feed phase surface and a tension phase surface. The feed phase surface engages the cam follower and pivots the pivoting roller carriage to actuate the strap feeding mechanism to engage a portion of a strap and feed the strap toward a strap application assembly where the strap is formed in a loop about a package. The strap feeding and tensioning mechanism actuates a first gripper that secures an end of the strap in the strap application assembly. The tension phase surface of the cam then engages the cam follower and pivots the pivoting roller carriage to actuate the strap tensioning mechanism to engage a portion of the strap and apply a tension to the looped strap. The strap feeding and tensioning apparatus also actuates a second gripper that secures the tensioned strap in a closed loop about the package so that the strap application assembly may form a strap joint sealing the strap in the closed loop. The apparatus automatically re-feeds a strap to the strap application assembly if the strap is not properly secured by the first gripper in the first instance. More specifically, the apparatus includes a strap stretch-out housing that receives strap retracted from the strap application assembly when the strap tensioning mechanism applies a tension to the strap. In the event that the strap is not properly engaged by the first gripper, the strap will be fully retracted from the strap application assembly and the strap will be directed into the strap stretch-out housing where it will remain until the feeding surface again engages the cam follower and pivots the pivoting roller carriage to actuate the strap feeding mechanism to engage a portion of the strap and re-feed the strap toward the strap application assembly. The weight and position of the strap disposed in the strap stretch-out housing prevents the strap from entirely withdrawing from the strap feeding mechanism, thereby ensuring that the strap feeding mechanism will engage and re-feed the strap to the strap application assembly.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following Detailed Description of the Invention with the accompanying drawings.